Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the full transparency burden. It discloses that the operation is a POST request, returns both hex and base64 signatures, costs $0.005 in USDC on Base, and requires payment via paymentTx or payerAddress (pointing to how_to_pay). This adds significant behavioral context beyond merely stating 'HMAC signature', though it omits error handling or rate limit details.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is two sentences: the first delivers the core functionality and request format, the second covers cost and payment. No filler words, no repetition of schema fields, and the most important information is front-loaded. Excellent conciseness.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The tool is simple with 5 optional parameters and no output schema. The description covers the request format, the output (hex/base64 signature), cost, and payment mechanism. It references how_to_pay for further detail, which is useful. It does not explicitly state the exact response JSON structure, but 'hex and base64 signature' sufficiently conveys the return format for an agent.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is only 40% (paymentTx and payerAddress are described; text, key, algorithm are not). The description partially compensates by showing an example payload with text/key/algorithm, making their roles somewhat clear (message, secret key, hash algorithm). However, it does not explicitly define each parameter, enumerate valid algorithms, or clarify optionality beyond the schema, leaving some ambiguity.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states 'HMAC signature' and provides a concrete request/response example (POST with text, key, algorithm -> hex and base64 signature). This definitively identifies the tool's function and distinguishes it from siblings like base64 or hash, which are non-keyed or purely encoding operations.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies when to use the tool (whenever an HMAC signature is needed) through its definition and example, but it does not explicitly contrast with alternatives such as 'hash' for non-keyed hashing or 'base64' for encoding. No explicit when-not-to-use guidance is provided, so it relies on the user inferring the appropriate context.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.